Used the 'llvm-readelf' utility to find details about the libraries linked with lldb binary and realised that the directories mentioned in RUNPATH might not have the required libraries.
Similar to reasons mentioned in my earlier issue "TestFoundation test suite failing while building Swift Toolchain", I manually copied the libraries and it worked. The lldb test suite was executed, though it fails now for only 7 test cases:-
Failing Tests (7):
LLDB :: SwiftREPL/ErrorReturn.test
LLDB :: tools/lldb-mi/symbol/symbol-list-lines.test
lldb-Suite :: lang/swift/dwarfimporter/C/TestSwiftDWARFImporterC.py
lldb-Suite :: lang/swift/reference_storage_types/TestSwiftReferenceStorageTypes.py
lldb-Suite :: lang/swift/repl_in_c/TestSwiftReplInC.py
lldb-Suite :: lang/swift/unknown_self/TestSwiftUnknownSelf.py
lldb-Suite :: lang/swift/variables/swift/TestSwiftTypes.py